Many people believe that skarner is underpowered, or useless, but they are wrong. He is very strong top lane, and end game is an unescapable opponent. Skarner has the the ability to harrass while healing himself consistantly, and can make amazing ganks as well as saves with his ult. He is a "diamond in the rough" so to speak. Skarner isnt about doing burst damage. Skarner is about sticking to 1 or more targets and finishing them at all costs.

The masteries I chose allow skarner to have great lane stayability, as well as do great damage. You may also take a 9/21/0 tree as an alternative if u go mana crystal first instead of dorans ring. Skarner has mana issues, so the utility tree is vital without the tear.

For marks I choose to go flat ad over armor pen simply for easier last hitting, and better harrass with his q ability. You may sway with armor pen marks if u wish, but in my experience skarner is better suited with flat ad

For seals I go dodge. Pretty simple reasoning: You are a top laner.... top laner's usually are not ability based, making dodge that much more usefull.

Glyphs for skarner are flat mana regen, for a great early game until u have your manamune. Feel free to swap with any glyphs, but i like to spam my abilities.

Quints are armor pen, with the flat ad maks, and the armor pen quints u will be doing true damage to minions, and add a little bit more "ooooommmf!" to your attacks.

Pros:
+good damage
+consistent aoe slow
+situational bad-*** tail spear
+when full build is done... they either run or they're dead

Cons:
-if built this way kinda squishy
-doesnt burst
-relys on good player judgement and skill

on skarner I start with either a dorans ring or a dorans blade. Your choice. On your first trip back you should have about 1350 gold and buy your tear of the goddess, and boots of speed. Now that you have your tear, feel free to walk up to your opponent and spam your q ability. Now that your mana problems are solved, its time to work on damage. Go back when you have 1275 gold, and get a hextech revolver, and a ward. No your e and q combo heals for almost 2x as much! now farm minions ( or kills if you're lucky ) until you have 1500 gold. Go back and get a pickaxe and a vampiric scepter. Now go farm up until you have enough for gunblade. Start building the parts for trinity force, and go from there. Whether you want more ap, more ad, or more survivability is up to you. Once your trinity and gunblade are done, you can perma-slow entire teams, and do decent damage. If someone happens to get away, remember to use the gunblade active! It's a free 50% slow!

Skarner is one of the most unique champions in the League, and can be one of the best if played correctly. His ratios are not the best, but they aren't supposed to be. He isn't meant to burst, and what I mean by this is that his skills per hit don't do very much, but used in succession do consistent dps. Hard to play well, but when he's mastered, Skarner is one of the most fun champions to play. Good luck and have fun :)